The present invention generally relates to semiconductor devices having thin film wiring layers and methods of forming thin film wiring layers, and more particularly to a semiconductor device having a thin film wiring layer made of aluminum containing carbon and a method of forming a thin film wiring layer made of aluminum containing carbon.
An integrated circuit is produced by forming elements on a semiconductor substrate and connecting the elements by a metal thin film wiring layer. The size of the elements and the wiring layer is reduced so as to increase the integration density of the integrated circuit, but presently, the integration density of the integrated circuit is limited by the limit in reducing the size of the wiring layer.
When the film thickness of the wiring layer is made extremely small, a disconnection of the wiring layer easily occurs at a stepped portion of the wiring layer. Furthermore, aluminum is normally used for the wiring layer, but the electromigration in the aluminum wiring layer increases with increasing current density and a void is easily generated in a portion of the aluminum wiring layer where the aluminum atoms lack. A disconnection occurs at such a portion of the aluminum wiring layer where the void is generated. On the other hand, a hillock is generated at a portion of the aluminum wiring layer where there are excessive the aluminum atoms, and the hillock easily causes a short-circuit between layers on the semiconductor substrate In addition, when the aluminum wiring layer is formed on a doped region of a silicon layer, for example, the aluminum easily diffuses into the doped region in the spike and short-circuits a junction between the silicon layer and the doped region.
The above described problems of the aluminum wiring layer are all caused by the fact that migrations easily occur in the case of aluminum atoms. The migration includes the electromigration and stress migration. While the electromigration is dependent on the current density, the stress migration is independent of the current density. A stress acts on the aluminum wiring layer from one or more layers in contact with the aluminum wiring layer, and the aluminum atoms are easily moved by this stress at high temperatures. Hence, when the aluminum wiring layer is cooled after being heated, a disconnection easily occurs in the aluminum wiring layer due to the stress. When a semiconductor device is produced, the semiconductor device is usually subjected to processes at high temperatures, and it is thus extremely difficult to suppress the stress migration in the aluminum wiring layer.
Accordingly, attempts have been made to eliminate the above described problems by using an aluminum alloy for the wiring layer, such as aluminum containing copper and aluminum containing silicon. However, when the aluminum containing copper is used as the wiring layer and this wiring layer is etched by a reactive ion etching (RIE) using chlorine gases, it has been found that copper residue remains at the surface of the wiring layer after the RIE and there is a problem in that it is difficult to remove this copper residue.
On the other hand, problems also occur when the aluminum containing silicon is used for the wiring layer, although silicon is prevented from diffusing into the wiring layer when the wiring layer made of the aluminum containing silicon is formed on a silicon layer. For example, when a silicon layer has an n.sup.+ -type doped region and the wiring layer also covers a contact hole located above and exposing the n.sup.+ -type doped region, a solid phase epitaxial growth of the silicon contained in the wiring layer occurs on the n.sup.+ -type doped region especially in a vicinity of the wall of the contact hole. But since this epitaxially grown silicon is of the p-type, a p-n junction is formed at the contact portion between the n.sup.+ -type doped region and the wiring layer thereon and increases the resistance and the contact portion.
In order to reduce the hillock which is generated in the aluminum wiring layer, there is a conventional semiconductor device having a plurality of aluminum wiring layers, with a metal layer interposed between two adjacent aluminum wiring layers. However, it is impossible to completely eliminate the hillock in the aluminum wiring layer, and the problems described before occur due to the generation of the hillock.
Therefore, there are demands for a wiring layer which can effectively contribute to the further increase in the integration density of the integrated circuit, and a method of forming such a wiring layer.